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spite of the fact that we have grown out, not only from that association but largely also from the “typhoid-fly” and “typhoid-milk” association into the remaining combination, as yet practically untouched from a control standpoint, the “typhoid-carrier.” Executives of health departments, if they wish to eliminate the residual typhoid, will need to engage in the social work phase of control of the activities of the recovered typhoid patient, until he is no longer a carrier. It is doubtful if tk+e energies of the health departments or the group discipline of the people a t large is great enough to achieve this result. Returning to our main thought, we can conclude that the safety factor in water quality is a demonstrated fact in most of our communities. The standard of sanitary quality is well known, the means of purification are well understood, and the results, except in some cities reluctant to emerge from their own stupidity, are effective in promoting health. Therefore, while desiring to assign true value to the safety factor, it is necessary to reserve sufficient weight for the remaining factors to obtain for them the consideration that they deserve. It thus seems proper to assign the bare majority weight, 51 per cent, to safety. It is the greatest factor, but not the only one. Next, in order, 22 per cent of the total 100 per cent rating will be assigned to taste. Not so tangible a factor as others, but one which reflects itself more than any other in the attitude of the water user toward the supply. And in these days, when the merchandizing phase of utility service is being more closely studied, the value of “state of mind” is looming larger than it did. The water department that, in order to make its supply safe, makes it repulsive to taste and stops there with the resigned feeling that nothing more can be done is not only in error as to the facts, but is creating a bad state of mind toward the supply that is dangerous when problems of financing reasonable extensions to the system are subject to review and approval by the public a t large. To the factor “chemical balance” will be assigned a value of 20 per cent. The demerit given to the corrosive tendency of water, on the one hand, or excessive hardness on the other, and the weight in the quality sum given for the correction of either one or the other, are minimized somewhat by the fact that the cost of correcting the defect is not generally accom-
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panied by any more than a corresponding saving in the individual expenditures required to repair damage. But its value grows upon observation of the attitude of communities where corrosion is checked or the water is softened. Water in “chemical balance” has a better sales value and is likely t o increase the rating as to safety, taste, and appearance. Appearance must be given weight in the rating scale. If water does not look good, the verdict of safety does not mean much. But since attainment of any one of the three above factors is likely to include good appearance, a possible value of 5 will be assigned t o this factor. Temperature has a bearing on quality, but is largely uncontrollable. It is therefore assigned a value of 2, or 2 times the percentage that would be added to sales in cities having a public water supply of high summer temperature, and a source for development of some private supplies of lower temperature. Thus, taking as a fair measure of value of the quality factor in public water supply of 30 points maximum out of 100 total, and dividing the 30 points among 5 factors on a 100 per cent basis, 51 per cent of quality can be assigned to safety, 22 per cent to taste, 20 per cent to chemical balance, 5 per cent to appearance, and 2 per cent to temperature. Such an evaluation makes it plain that safe water is the first factor in quality, but only one of several, that the reaction of the individual when drinking water is a very important one, that water that is safe and tastes good, but is either corrosive or hard, is not rated high in the quality scale, and that appearance and temperature have their weight. Those engaged in the production of public water supplies will do good service to themselves and their patrons, if they consider seriously the rating that their supply would deserve on such a quality basis. They can then adjust the conceptions they may have of its total quality value, and proceed to recast their improvement program in the light of the relative values of the demerit points. At no time should one lose sight of the fact that the users of a supply needing improvement may not appreciate the needs, and it will be just as necessary to educate them to the point of willingly supporting the financial problem involved, as first to have convinced the managers of the supply as to the propriety of the investment.
Superchlorination and Subsequent Dechlorination over Carbon of Water for Municipal Supply’ Ernst Watzl WATZL-SCHWBITZER, INC.,HURON-SIXTH BUILDING, CLEVELAND. OHIO
GREAT many authorities on water purification and many practical engineers advocate superchlorination of water, with subsequent dechlorination (sulfur dioxide, ammonia, potassium permanganate, etc.). They know what risks are taken in using inadequate amounts of chlorine, which means that harmful substances (bacteria) and much organic matter as nutrient for bacteria are left in the water. The organic matter in the water also accounts for the difference usually found in bacterial counts a t the place where the water is treated and the more distant outlets (aftergrowth). In 1926 there were eighteen more or less serious epidemics in
A
I Received August 30, 1928. Presented before the Division of Water, Sewage, and Sanitation at the 76th Meeting of the American Chemical Society, Swampscott, Mass., September 10 to 14, 1928.
Central Europe. The most severe epidemic occurred in Hanover, Germany, in September. This city takes its water supply from various sources, one of which is a battery of wells. The water is treated and disinfected by the method standard in the United States-namely, chemical treatment, mechanical filtration, and chlorination, the average addition for the period involved having been approximately 0.8 p. p. m. of chlorine. During a heavy rainfall a small creek near the battery of wells left its banks and flooded part of the wells. The content of organic substances jumped up to about six times the normal, so that the added, amount of chlorine was consumed immediately by the organic matter, leaving nothing to destroy the also enormously increased bacteria count. For only 2l/1 hours heavily contaminated water was pumped into the combined water mains. This resulted in the death
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INDUSTRIAL AND ENGINEERING CHEMISTRY
of about 1800 citizens and the illness of over 60,000. It remained a menace to the community for seven years as a germ carrier. Hanover had had no epidemic for forty-six years and was considered one of the best cities in Germany with respect to general sanitary conditions. The waterworks director committed suicide and a committee of experts from all the large countries in Europe was called to Hanover to investigate the disaster and its sources. The investigation showed that the waterworks officials could not be held responsible. They had proceeded according to the methods then accepted as standard. It was proved, however, that the added amount of chlorine had not been sufficient for this extraordinary occasion. According to the explosion theory of epidemics put forward by modern epidemiologists, the great danger in water occurs in the fluctuation in bacterial count. It is believed that no water can be considered safe until the possibility of such fluctuations is eliminated, as a modern rapid sand filtration plant takes care only of part of these fluctuations. If, on the other hand, the engineers in charge proceed more conscientiously and add enough chlorine t o avoid such dangers, the water furnished may be unpalatable, have an obnoxious odor and taste, and be irritating to the skin of many susceptible individuals. This explains the many efforts in Toronto, Canada, London, England, and other cities to remove the excess chlorine. Unfortunately, the first attempts a t dechlorination were made by adding other chemicals (SO*, etc.) to drinking water, thus merely doubling the hazard of correct dosage. Chemical removal involves also the installation and operation of complicated equipment for distributing, mixing, controlling, and testing.
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while the other objectionable organic chlorine compounds are either adsorbed or oxidized t o higher decomposition products, rendering the water free from taste and odor. It is rather difficult to analyze precisely the action of free or active chlorine on the various ‘Lorganicsubstances” in water, because the chemical composition of these compounds is not yet completely known. Adler’s thorough investigations and experiments have shown that, in practicing high chlorination, the urea from human and animal wastes is completely decomposed into nitrogen and carbon dioxide, that the so-called albuminoid-nitrogen can be reduced to negligible traces, and that the “human substances” are as a rule almost completely oxidized. The substances of the indole and skatole groups derived from vegetable and animal waste products are also destroyed. Experience during many years with hundreds of different waters has shown that, in order to make water safe, from 0.2 to 0.5 p. p. m. of free or residual chlorine should be present after sand filtration, followed by chlorination and a detention period (contact) of 10 minutes to one-half hour, before it is allowed to enter the dechlorinator. The figures for residual chlorine, as well as the detention period, are in direct relation and can be altered to suit special conditions. For instance, should it be impossible to build large clear wells so that no guarantee could be given with respect to longer contact periods, the residual chlorine should be kept a t 0.5 part per million. This holds also with waters showing great fluctuations in the content of “organic substances.” It will be advisable to go even higher with very poor waters in order to guarantee safety and palatability. The dechlor process is used in conjunction with an automatic and registering chlorine indicator (Bloch, Dresden, Louben, Germany), which shows continuously the amount American Dechlor Process of residual chlorine just before the water enters the dechloIt has been found that if water containing an excess of rinator. This indicator, on the other hand, is in controlling free chlorine is led under certain operating conditions through connection with the chlorine discharge equipment. Should a bed of carbonaceous material the free chlorine combines the residual chlorine drop below the demanded amount with the carbon and leaves the “dechlorinator” without a the discharge is automatically opened, until the residual chlorine content reaches the demanded height. Analyses trace of free chlorine. With respect to the removal of the taste and odor coming made even every hour would not insure such safety. Flucfrom the chlorinated phenol groups, it is well known that tuations of chlorine-consuming substances or operating oxybenzenes, naphthols, and anthracene derivatives, tar, troubles with the chlorine-distributing equipment are thus creosote oils, and the like, which after chlorination cause the taken care of. Insufficient oxidation (aeration or chlorination) will leave well-known obnoxious taste and odor, after high chlorination give higher substituted aromatic chlorine derivatives, which unprecipitated iron and manganese salts in the water. It is as a rule, have either no smell or only a slight smell. On the well known that in various filter plants which are troubled other hand, high chlorination and therefore large amounts of with manganese salts, even in those that use prechlorination hypochlorous acids have the property of breaking up the and aeration, the iron oxide contained in the gravel of the benzene nucleus of many isocyclic compounds which have one filter beds acts as a catalyst, precipitating the colloidally suspended manganese salts onto the sand filters in the form of or more hydroxyl groups in their nuclei. The carbon dechlorinator is highly adsorptive to the or- manganese dioxide, coloring them pitch-black. The wellganic substances mentioned. Therefore that part of the known process of inserting a bed of iron oxide, together with chlorination products of the phenol group which has not superchlorination, will eliminate all iron and manganese salts been converted into tasteless and odorless compounds by the from the treated water. high chlorination is partly held back in the dechlorinator and Not every charcoal can be used economically in this process. partly further oxidized by the high concentration of chlorine Only granular charcoal with highly adsorptive qualities for in the carbon bed (condensed on the carbon particles), thus chlorine as well as for organic chlorine compounds is suitable safely ensuring a tasteless and odorless effluent. for this purpose. Ordinary charcoal used for burning, in As there are fluctuations in the content of microorgan- order to accomplish complete conversion of the free chlorine, isms, there are times when even highly contaminated water would have to be used in such a great depth that the resulting shows few phenols, if any. During these periods the chloro- loss of head, as well as large reservoirs to hold such material, phenols accumulated in the carbon bed by the absorbed -would make its use practically impossible. chlorine are oxidized and leave the carbon bed ready for new The research work in the United States with superchlorinaadsorption and oxidation of chlorophenols. tion and subsequent dechlorination has been made possible The main object of the American dechlor process is to mainly by the aid of City Manager Hopkins of Cleveland, convert fluctuations of harmful organic constituents in the Ohio. As a result of this work, a semicommercial plant for water into varying residual chlorine, which is taken care of the treatment of 300,000 gallons daily, for establishing comby the carbon bed, independent of chlorine concentration, plete data for the construction of additional equipment for
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the Cleveland water supply, was completed in February, 1928. The American Water Works and Electric Supply Company is also carrying on tests on a semicommercial basis. The Candy Filter Corporation, London, England, has successfully used a dechlor process over carbon for the past eighteen years. 2 J . ROY.I n s t . Pub. Health, 19 (1911); Surncyor, 49 (December 16,1910); Engineer, 19 (January 6, 1911).
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Acknowledgment
The writer takes this opportunity to express his gratitude for the valuable information he has received, either from articles in the literature or through personal communication, from F. Pullen Candy, Sir Alexander Houston, J. W. Elllms, Rudolph Adler, w. c. Lawrence, P~ofessorJackson, Mr. Tarvett, Abel Wolman, Linn H. Enslow, and N. K. Chaney.
Diffusion of Water through Rubber' Earle E. Schumacher and Lawrence Ferguson BELLTELEPHONE LABORATORIES, 463 WESTSr., NEW YORP,N. Y.
T HAS long been known that rubber sheets are not impervious to either gases or water. As early as 1830 J. K.
A thin glass capsule containing water for the test was placed in one chamber and both chambers were then evacuated to Mitchell: a Philadelphia physician, studied the problem. a pressure of approximately 0.01 mm. of mercury for a t least He and later investigator^,^^^ 6 however, were chiefly concerned 20 hours. After the capsule was broken, the amount of with determining the relative rates of diffusion of many sub- water which passed through the membrane was measured from stances through some particular thin rubber membrane. In time to time, either by a mercury manometer observed the present study attention has been centered on the deter- through a micrometer microscope or gravimetrically by obmination of the rate of diffusion of one substance, water, serving the extension of a calibrated quartz fiber spring8 to through rubber of several different compositions. which was attached a light basket containing phosphorus pentoxide. Throughout the tests the apparatus was kept Apparatus and Method in a thermostat a t 25.0' * 0.1" C. A very essential element of any diffusion-measuring apThe evacuation removed most of the sorbed gas and water paratus is a leakproof seal from the rubber membrane between the test membrane and the inside of the a p The diffusion of water through thirteen rubbers of and the chambers on each paratus. In the gravimetric different compositions has been measured. The data side. Preliminary work in procedure any water vapor obtained by two different methods are in satisfactory measuring the rate of diffuremaining after the evacuaagreement. sion of water through varition was absorbed by the The mathematical derivation of a simple formula for ous types of rubber showed phosphorus pentoxide becalculating the rate of diffusion has been given. fore the water capsule was that the ordinary seals using The diffusion measurements have shown: (a) that broken. With the manomwax, cement, and similar the rate of diffusion of water through a rubber memeter method the pressure substances probably would brane is inversely proportional to the square of the indicated after the capsule be s a t i s f a c t o r y only for thickness; ( b ) that the rate of diffusion decreases was broken was the commembranes through which greatly with increase in hardness; ( c ) that the effect bined result of water vapor d i f f u s i o n is v e r y rapid. of saturating the rubber with water is to increase that diffused through the With o t h e r m e m b r a n e s the rate of diffusion through it, due probably not only rubber and small amounts these sealing materials to an increase in the water vapor pressure within the of residual gas and vapor u su a l l y c a u s e trouble by rubber, but also to a decrease in hardness; ( d ) that gradually given off by the gradual crystallization and there is no intimate relationship between rate of difrubber. (Blanks and parconsequent leakage, evolufusion and minor variations in the composition of the allel tests made w i t h o u t tion of gas, failure to adhere rubber. breaking the capsule showed to the apparatus, or cold that the amounts of residual flow. I n o r d e r t o a v o i d gas and vapor were small.) these troubles a mecia1 aDparatus combining a mechanical clamp and a mercury seal The magnitudes of the gas and water-vapor components were was developed, by means of which an air-tight chamber could easily found by freezing out the water vapor a t -45' C. with be connected to each side of the test membrane. Flanges melting monochlorobenzene while the residual gas pressure were provided on the two chambers with which to fasten the was measured. The freezing mixture reduced the vapor presedge of the membrane, and a ball-bearing screw device sure of the water to approximately 0.06 mm. of mercury and did clamped the parts together without any appreciable torsion not appreciably affect the small pressures of carbon dioxide, on the rubber. An enclosed space about the membrane joint sulfur dioxide, nitrogen, oxygen, and other gases likely to was filled with mercury. A detailed description of this ap- have been present. (The pressures of these gases were always far below those necessary to cause liquefaction a t paratus has been published elsewhere.' -45' C., and only a negligible quantity could dissolve in the 1 Received August 18, 1928. frozen water.) * J. Med. Sci., 13, 36 (1830).
I
Graham, Phil. Mag., 34, 401 (1866). Dewar, Proc. Roy. Znst. GI. Brit., 41, 558, 813 (1915). 6 Daynes, Proc. Roy. Soc. (London), 9TA, 286 (1920). 8 Edwards and Pickering, Chem. Met. Eng., 23, 17, 71 (1920). They tested many different membranes but for all practical purposes they were very nearly alike, as their discussion shows. 7 Schumacher and Ferguson, J . A m . Chem. Soc., 49, 427 (1927). 3
Theoretical
4
DESCRIPTION OF DIFFUSION PRocEss-After the diffusion of water through rubber had been studied for some time, a 8
McBain and Baker, J . A m . Chem. Soc., 48,690 (1926).
